The overall aim of this project is to increase the transport of microorganisms through subsurface environments to facilitate the introduction of novel metabolic traits and the degradation of widely dispersed environmental pollutants. To achieve this aim, we will concentrate our efforts on three tasks: (1) enhance microbial transport by modifying the surface of the cell to reduce attachment to soil particles (Enhanced transport); (2) examine the effect of low water velocities and flow through water-unsaturated media on microbial transport, (Vadose zone transport); (3) conduct large-bore soil column and lysimeter experiments to determine if results of soil column experiments are accurate and predictive of large scale processes (Scaling study). There will be a complimentary modeling component for three tasks of this project. Our focus on transport through unsaturated media is in keeping with the overall theme for the hydrology component of our hazardous-waste center. The site core, which will consist of intermediate-scale facilities for integrated transport, chemical and biological experiments, will give us the ability to undertake vadose-zone studies at larger scales. The other two hydrology projects, which involve studying transport of trace metals and organic contaminants in the presence of natural-organic matter colloids, also will have a vadose-zone emphasis.